it('calculates total with discount', () => {
  // Arrange - set up test data
  const cart = new ShoppingCart();
  cart.addItem({ name: 'Book', price: 20 });
  cart.applyDiscount(0.1);

  // Act - execute the code under test
  const total = cart.getTotal();

  // Assert - verify the result
  expect(total).toBe(18);
});

// ✅ Describes behavior and scenario
describe('UserService.register', () => {
  it('creates user with hashed password', () => {});
  it('throws ValidationError when email is invalid', () => {});
  it('sends welcome email after successful registration', () => {});
});

// ❌ Vague names
it('test1', () => {});
it('should work', () => {});

// ✅ Each test sets up its own data
beforeEach(() => {
  mockRepository = { save: jest.fn(), find: jest.fn() };
  service = new OrderService(mockRepository);
});

// ❌ Shared state between tests
let globalOrder: Order; // Tests depend on each other

        /\
       /  \      E2E Tests (few)
      /----\     - Test critical user flows
     /      \    - Slow, expensive
    /--------\   Integration Tests (some)
   /          \  - Test component interactions
  /------------\ - Database, API calls
 /              \ Unit Tests (many)
/----------------\ - Fast, isolated
                   - Test single units

file:line - [category] Description of issue

tests/user.test.ts:15 - [struct] Missing Arrange/Act/Assert separation
tests/order.test.ts:42 - [iso] Test depends on previous test's state
tests/cart.test.ts:28 - [assert] Multiple unrelated assertions in one test

rules/struct-aaa-pattern.md
rules/iso-independent-tests.md
rules/data-factories.md